diff --git a/src/calibre/manual/customize.rst b/src/calibre/manual/customize.rst
index e5635d5165..f875b0e648 100644
--- a/src/calibre/manual/customize.rst
+++ b/src/calibre/manual/customize.rst
@@ -19,12 +19,20 @@ use *plugins* to add funtionality to |app|.
 Environment variables
 -----------------------
 
-    * ``CALIBRE_CONFIG_DIRECTORY``
-    * ``CALIBRE_OVERRIDE_DATABASE_PATH``
-    * ``CALIBRE_DEVELOP_FROM``
-    * ``CALIBRE_OVERRIDE_LANG``
-    * ``SYSFS_PATH``
-    * ``http_proxy``
+    * ``CALIBRE_CONFIG_DIRECTORY`` - sets the directory where configuration files are stored/read.
+    * ``CALIBRE_OVERRIDE_DATABASE_PATH`` - allows you to specify the full path to metadata.db. Using this variable you can have metadata.db be in a location other than the library folder. Useful if your library folder is on a networked drive that does not support file locking.
+    * ``CALIBRE_DEVELOP_FROM`` - Used to run from a calibre development environment. See :ref:`develop`.
+    * ``CALIBRE_OVERRIDE_LANG`` - Used to force the language used by the interface (ISO 639 language code)
+    * ``SYSFS_PATH`` - Use if sysfs is mounted somewhere other than /sys
+    * ``http_proxy`` - Used on linux to specify an HTTP proxy
+
+Tweaks
+------------
+
+Tweaks are small changes that you can specify to control various aspects of |app|'s behavior. You specify them by editing the 2tweaks.py file in the config directory.
+The default tweaks.py file is reproduced below
+
+.. literalinclude:: ../../../resources/default_tweaks.py
 
 
 A Hello World plugin